1. Field of the Invention
This invention pertains to the field of modulation of immune responses such as those induced by genetic vaccines.
2. Background
Antigen processing and presentation is only one factor which determines the effectiveness of vaccination, whether performed with genetic vaccines or more classical methods. Other molecules involved in determining vaccine effectiveness include cytokines (interleukins, interferons, chemokines, hematopoietic growth factors, tumor necrosis factors and transforming growth factors), which are small molecular weight proteins that regulate maturation, activation, proliferation and differentiation of the cells of the immune system. Characteristic features of cytokines are pleiotropy and redundancy; that is, one cytokine often has several functions and a given function is often mediated by more than one cytokine. In addition, several cytokines have additive or synergistic effects with other cytokines, and a number of cytokines also share receptor components.
Due to the complexity of the cytokine networks, studies on the physiological significance of a given cytokine have been difficult, although recent studies using cytokine gene-deficient mice have significantly improved our understanding on the functions of cytokines in vivo. In addition to soluble proteins, several membrane-bound costimulatory molecules play a fundamental role in the regulation of immune responses. These molecules include CD40, CD40 ligand, CD27, CD80, CD86 and CD150 (SLAM), and they are typically expressed on lymphoid cells after activation via antigen recognition or through cell-cell interactions.
T helper (TH) cells, key regulators of the immune system, are capable of producing a large number of different cytokines, and based on their cytokine synthesis pattern TH cells are divided into two subsets (Paul and Seder (1994) Cell 76: 241-251). TH1 cells produce high levels of IL-2 and IFN-γ and no or minimal levels of IL-4, IL-5 and IL-13. In contrast, TH2 cells produce high levels of IL-4, IL-5 and IL-13, and IL-2 and IFN-γ production is minimal or absent. TH1 cells activate macrophages, dendritic cells and augment the cytolytic activity of CD8+ cytotoxic T lymphocytes and NK cells (Id.), whereas TH2 cells provide efficient help for B cells and they also mediate allergic responses due to the capacity of TH2 cells to induce IgE isotype switching and differentiation of B cells into IgE secreting cell (De Vries and Punnonen (1996) In Cytokine regulation of humoral immunity: basic and clinical aspects. Eds. Snapper, C. M., John Wiley & Sons, Ltd., West Sussex, UK, p. 195-215). The exact mechanisms that regulate the differentiation of T helper cells are not fully understood, but cytokines are believed to play a major role. IL-4 has been shown to direct TH2 differentiation, whereas IL-12 induces development of TH1 cells (Paul and Seder, supra.). In addition, it has been suggested that membrane bound costimulatory molecules, such as CD80, CD86 and CD150, can direct TH1 and/or TH2 development, and the same molecules that regulate TH cell differentiation also affect activation, proliferation and differentiation of B cells into Ig-secreting plasma cells (Cocks et al. (1995) Nature 376: 260-263; Lenschow et al. (1996) Immunity 5: 285-293; Punnonen et al. (1993) Proc. Nat'l. Acad. Sci. USA. 90: 3730-3734; Punnonen et al. (1997) J. Exp. Med. 185: 993-1004).
Studies in both man and mice have demonstrated that the cytokine synthesis profile of T helper (TH) cells plays a crucial role in determining the outcome of several viral, bacterial and parasitic infections. High frequency of TH1 cells generally protects from lethal infections, whereas dominant TH2 phenotype often results in disseminated, chronic infections. For example, TH1 phenotype is observed in tuberculoid (resistant) form of leprosy and TH2 phenotype in lepromatous, multibacillary (susceptible) lesions (Yamamura et al. (1991) Science 254: 277-279). Similarly, late-stage HIV patients have TH2-like cytokine synthesis profiles, and TH1 phenotype has been proposed to protect from AIDS (Maggi et al. (1994) J. Exp. Med. 180: 489-495). Furthermore, the survival from meningococcal septicemia is genetically determined based on the capacity of peripheral blood leukocytes to produce TNF-α and IL-10. Individuals from families with high production of IL-10 have increased risk of fatal meningococcal disease, whereas members of families with high TNF-α production were more likely to survive the infection (Westendorp et al. (1997) Lancet 349: 170-173).
Cytokine treatments can dramatically influence TH1/TH2 cell differentiation and macrophage activation, and thereby the outcome of infectious diseases. For example, BALB/c mice infected with Leishmania major generally develop a disseminated fatal disease with a TH2 phenotype, but when treated with anti-IL-4 mAbs or IL-12, the frequency of TH1 cells in the mice increases and they are able to counteract the pathogen invasion (Chatelain et al. (1992) J. Immunol. 148: 1182-1187). Similarly, IFN-γ protects mice from lethal Herpes Simplex Virus (HSV) infection, and MCP-1 prevents lethal infections by Pseudomonas aeruginosa or Salmonella typhimurium. In addition, cytokine treatments, such as recombinant IL-2, have shown beneficial effects in human common variable immunodeficiency (Cunningham-Rundles et al. (1994)N. Engl. J. Med. 331: 918-921).
The administration of cytokines and other molecules to modulate immune responses in a manner most appropriate for treating a particular disease can provide a significant tool for the treatment of disease. However, presently available immunomodulator treatments can have several disadvantages, such as insufficient specific activity, induction of immune responses against, the immunomodulator that is administered, and other potential problems. Thus, a need exists for immunomodulators that exhibit improved properties relative to those currently available. The present invention fulfills this and other needs.